1. Field of the Invention
The present invention is related with a stereo surround system which expands the stereo reproduction sound field.
2. Description of the Related Art
There are various types of audio visual apparatuses. In order to make more real the feeling of concert hall presence of reproduction sound seized as the listener's spatial impression, various sound field reproduction (or creation) technologies are developed. This is known as a surround system. "A feeling of the expanded or spread sounds" is one of the sensuous elements for reproducing the feeling of concert hall presence of sound. The stereo reproduction sound field expansion apparatus (hereinbelow, it is called as a stereo surround system) is known as signal process means for expressing this feeling of spread sound.
A stereo reproduction apparatus using a stereo wide circuit will be explained as an example of this stereo surround system, hereinbelow.
The process unit which expands the sound field in the horizontal direction, consists of the stereo wide circuit in this stereo reproduction apparatus. The right channel stereo audio signal (hereinbelow, it is called as a right signal R) and the left channel stereo audio signal (hereinbelow, it is called as a left signal L) which should be reproduced, are inputted into the process unit which expands the sound field in the horizontal direction.
A horizontal direction sound field expansion process unit, that is to say, a process unit for expanding the sound field in the horizontal direction, picks up the delay component and the reverberation component between the channels originally included in the inputted right signal R and left signal L, as a difference signal between the channels, and gives a phase delay process to this picked up difference signal, by a phase delay circuit etc. Then, it adds the processed signal, by arbitrary ratios to the original right signal R and the original left signal L, respectively, and outputs them as an expanded right signal RW and an expanded left signal LW, which will create pseudo-expanded sound.
The expanded right signal RW and expanded left signal LW are power-amplified respectively by an amplifier, and are supplied to a corresponding right speaker SPR and a corresponding left speaker SPL. At this time, the sound emitted from the right speaker SPR and the left speaker SPL reaches both of listeners' ears. The sound acts so that a listener may feel the sound which is spread wider in the right and left direction than the actual arrangement interval of the right speaker SPR and the left speaker SPL.
For example, there are Japanese Patent Publication No. (Hei) 3-12520, Japanese Patent Publication No. (Hei) 3-8640, etc. disclosing such a stereo wide circuit.
In this manner, the feeling of the spread sounds to the right and left direction can be obtained by the reproduction sound of a stereo surround system. However, the feeling of the spread sounds to the direction other than the right and left direction cannot be obtained by the above mentioned techniques. Therefore, as compared with the real case where the listener listens to an actual live performance etc., the above mentioned apparatus has the problem that a feeling of the spread sounds is not really obtained.